Mineral fiber forming device

ABSTRACT

A mineral fiber forming device including: a centrifuge configured to rotate about a rotation axis, the centrifuge including an annular wall pierced by a plurality of orifices, the axis of symmetry of the annular wall being the rotation axis; a first annular inductor configured to heat a top part of the annular wall; a second annular inductor configured to heat a bottom part of the annular wall. The device makes it possible to increase its energy efficiency and very greatly reduce, even cancel altogether, its carbon dioxide emission level.

The invention relates to a device for forming mineral fibers by aninternal centrifuging method. It applies in particular to the industrialproduction of glass wool that is intended to be used, for example, inthe composition of thermal and/or acoustic insulation products.

Different internal centrifuging methods are known. A molten glass threadis introduced into a fiberizing spinner rotating at high speed andpierced at its periphery by a very great number of orifices throughwhich the glass is sprayed in the form of filaments under the effect ofthe centrifugal force. These filaments can then be subjected to theaction of an annular drawing current at high temperature and speed alongthe wall of the centrifuge, a current that thins them and transformsthem into fibers. The fibers that are formed are driven by this gaseousdrawing current to a receiving device generally consisting of agas-permeable receiving and conveying mat.

This method has been the subject of numerous refinements, relating inparticular, for some, to the fiberizing spinner, for others, to themeans of generating the annular drawing current, for example by the useof burners of particular type. See in particular the documents EP-B-0189 354, EP-B-0 519 797, WO-A-97/15532 regarding the latter point.

The document FR-A-1 382 917 describes a fiberizing member, the principleof which is still abundantly used: the molten material is brought into abasket comprising, on its vertical wall, orifices through which thematerial is sprayed onto the wall of a fiberizing spinner which isattached to the basket and which comprises a large number of orifices.This wall is called the “strip” of the fiberizing spinner. In order toobtain quality fiber production, the orifices are distributed on annularrows and the diameters of the orifices are variable depending on the rowto which they belong, this diameter decreasing from the top of the stripto its bottom part.

Enhancements have been made to this basic principle, as taught inparticular in the document FR-A-2 443 436, in which means make itpossible to obtain a laminar flow of the molten material from top tobottom of the strip of the spinner.

Another modification, described in the document EP-A-1 370 496, has beenmade to enhance the quality of the fibers and increase the efficiency.This modification entails distributing the orifices of the strip in aplurality of annular areas arranged one above the other, with at leasttwo annular areas having a number of orifices per unit of surface areawhich is different by a value greater than or equal to 5%.

The document WO 03/069226 describes an internal combustion burnercomprising a combustion chamber into which opens at least one fuel andoxidant feed duct and at least one flame stabilizing element creating acontainment area in which at least a portion of the combustion takesplace.

In all these examples, the peripheral strip of the spinner is heatedboth by the molten glass which is centrifuged in the fiberizing spinnerand by the hot air blown by an internal combustion burner generating theannular drawing current.

However, the heating by an internal combustion burner is a source ofsignificant energy consumption, with an energy efficiency less than 30%,and a source of very high carbon dioxide emissions.

There is therefore a need for a mineral fiber forming device which hasan energy consumption and a carbon dioxide emission level that are bothreduced.

For this, the invention proposes a mineral fiber forming devicecomprising:

-   -   a centrifuge suitable for rotating about a rotation axis, the        centrifuge comprising an annular wall pierced by a plurality of        orifices, the axis of symmetry of the annular wall being the        rotation axis,    -   a first annular inductor suitable for heating the top part of        the annular wall,    -   a second annular inductor suitable for heating the bottom part        of the annular wall.

According to another particular feature, the mineral fiber formingdevice also comprises a first blowing ring suitable for blowing air overthe mineral fibers that are about to leave through the plurality oforifices in the annular wall so as to drive them to a fiber receivingand conveying mat.

According to another particular feature, the mineral fiber formingdevice also comprises a second blowing ring suitable for blowing airover an area of the centrifuge situated above the annular wall so as tocontrol the temperature of the top part of the centrifuge.

According to another particular feature, the cooperation of the twoblowing rings creates an area of turbulences in proximity to the annularwall of the centrifuge, this area of turbulences allowing for anadditional drawing of the mineral fibers that are about to leave throughthe plurality of orifices in the annular wall.

According to another particular feature, the device also comprises atleast two first concentric blowing rings of different diameters, thecooperation of the first blowing rings creating an area of turbulencesin proximity to the annular wall of the centrifuge, this area ofturbulences allowing for an additional drawing of the mineral fibersthat are about to leave through the plurality of orifices in the annularwall.

According to another particular feature, the first annular ringcomprises a plurality of concentric air outlets creating an area ofturbulences in proximity to the annular wall of the centrifuge, thisarea of turbulences allowing for an additional drawing of the mineralfibers that are about to leave through the plurality of orifices in theannular wall.

According to another particular feature, the second annular inductor,for example situated under the centrifuge, is connected in series or inparallel with the first annular inductor. The first and second inductorsare then preferably powered independently of one another.

According to another particular feature, the mineral fiber formingdevice also comprises an internal burner suitable for use on starting upthe mineral fiber forming device.

According to another particular feature, the centrifuge comprises abottom.

According to another particular feature, the centrifuge does notcomprise a bottom and comprises a basket.

According to another particular feature, the mineral fiber formingdevice also comprises a mineral fiber gluing ring situated under thecentrifuge.

The invention also relates to a method for forming mineral fibers byinternal centrifuging, implementing the device described above, in whichthe material to be turned into fiber is poured into the centrifuge.

Other features and advantages of the invention will now be described inlight of the drawings in which:

FIG. 1 represents a cross-sectional view of a mineral fiber formingdevice according to the invention.

“Up”, “down”, “above” and “under” are defined in relation to a verticalaxis when the centrifuge is in the centrifuging position, that is to saywhen the rotation axis of the centrifuge is on a vertical axis, as inFIG. 1.

The invention relates to a mineral fiber forming device. The devicecomprises a centrifuge suitable for rotating about a rotation axis. Thecentrifuge comprises an annular wall, whose axis of symmetry is therotation axis, which is pierced by a plurality of orifices. The devicealso comprises first and second annular inductors. The first annularinductor is suitable for heating the top part of the annular wall of thecentrifuge. The second annular inductor is suitable for heating thebottom part of the annular wall of the centrifuge.

Thus, the heating of the centrifuge is carried out by electricalinduction, which makes it possible to increase the energy efficiency andvery greatly reduce, even cancel out altogether (if no internal burneris used), the carbon dioxide emission level, since no annular internalcombustion burner producing a flow of hot gas is used.

FIG. 1 represents a cross-sectional view of a mineral fiber formingdevice according to the invention.

The mineral fiber device comprises a centrifuge 1, also calledfiberizing spinner, comprising an annular wall pierced by a plurality oforifices 11. The centrifuge 1 also comprises a web 13. The web 13 formsthe top of the centrifuge 1, between the annular wall and the tulip. Themineral fiber forming device also comprises a shaft 15 of axis 9intended to be driven in rotation by a motor (not represented). Thecentrifuge 1 is fastened to the shaft 15 via the tulip, which is in theextension of the web. When the mineral fiber forming device is in thefiberizing position, the axis 9 is vertical. The axis 9 is the axis ofsymmetry of the centrifuge.

The shaft 15 is hollow. At its top end, the shaft 15 is linked to moltenglass feeding means. At its bottom end, the shaft 15 is linked to thecentrifuge when the latter is provided with a bottom, as can be seen inFIG. 1. As a variant, if the centrifuge 1 does not have a bottom, theshaft 15 is linked to a basket. In the case of a device with basket, thebasket is situated inside the centrifuge 1, which is itself fastened tothe shaft 15. The basket, also fastened to the shaft 15, is intended tobe driven in rotation with the centrifuge 1 and the shaft 15. The basketcomprises an annular wall pierced by a plurality of orifices.

When the mineral fiber forming device is in operation, the centrifuge 1and the shaft 15, as well as, if appropriate, the basket, are driven inrotation about the axis 9 of the shaft 15. Molten glass 6 flows into theshaft 15, from the molten glass feeding means, to the bottom of thespinner or into the basket, wherein the molten glass 6 spreads. In thecase of a centrifuge with bottom, a permanent reserve of molten glass 6is formed against the annular wall 10 under the effect of the rotation.In the case of a centrifuge without bottom and with basket, the moltenglass is sprayed, under the effect of the rotation, onto the annularwall of the basket, passes through the plurality of orifices in thebasket and, in the form of bulky filaments, is sprayed onto theperipheral wall 10 of the centrifuge 1. A permanent reserve of moltenglass 6 is then formed in the centrifuge without bottom against theannular wall under the effect of the rotation. The permanent reserve ofmolten glass 6 feeds the plurality of orifices 11 pierced in the annularwall 10 of the centrifuge 1 to form flow cones that extend to becomepre-fibers.

The orifices 11 in the annular wall 10 of the centrifuge 1 arepreferably more numerous and of smaller diameter than the orifices of anannular wall of a centrifuge used with an internal combustion burnerbecause the drawing is less effective with induction heating than withheating by internal combustion burner. Thus, the annular wall 10 of thecentrifuge 1 preferably comprises between 5000 and 25 000 orifices andthe orifices 11 preferably have a diameter of between 0.2 mm and 0.5 mmfor a spinner diameter of 200 mm.

The mineral fiber forming device also comprises a first annular inductor2 suitable for heating the top part of the annular wall 10 of thecentrifuge 1. The first annular inductor 2 can also be suitable for alsoheating the web 13 of the centrifuge 1. The first annular inductor 2 is,for example, arranged above the centrifuge 1, in proximity to the web 13and the annular wall 10. The first annular inductor 2 consists, forexample, of coils comprising between one and four copper turns, forexample between two and four copper turns. The annular inductor 2 ispreferably provided with field concentrators, for example made offerrite, which make it possible to direct the magnetic field toward thespinner in order to heat only the spinner and, thus, protect the othermetal parts of the device. The annular inductor 2 makes it possible toheat the annular wall to a temperature of between 1000 and 1200° C.

The mineral fiber forming device also comprises a second annularinductor 5 suitable for heating the bottom part of the annular wall 10of the centrifuge 1. The second annular inductor can also be suitablefor also heating the area of the centrifuge situated below the annularwall 10. The second annular inductor 5 is, for example, situated underthe centrifuge. The second annular inductor 5 consists, for example, ofcoils comprising between one and four copper turns, for example betweentwo and four copper turns. The annular inductor 5 is preferably providedwith field concentrators, for example made of ferrite, which make itpossible to direct the magnetic field toward the spinner in order toheat only the spinner and, thus, protect the other metal parts of thedevice. The assembly of the two annular inductors 2 and 5 has, forexample, a power of 20 to 150 kW, for example 20 to 70 kW.

The operating frequency of the first and second annular inductors 2, 5is, for example, between 1 and 300 kH.

The second annular inductor 5 is, for example, connected with the firstannular inductor 2, in series or in parallel, so that the magneticfields of the first and second annular inductors 2, 5 are in phase toavoid the mutual effects or the phase-shifted fields which cancel oneanother out.

As a variant, the first and second annular inductors 2, 5 are powered bytwo independent circuits, preferably powered independently in order tobe able to control and regulate their power independently. Thegenerators are such that the effects of mutuality have to be avoided or,at least, limited.

The heating of the annular strip by two different areas (top and bottom)makes it possible to have a temperature gradient over the height of thecentrifuge 1. This makes it possible to control the viscosity of theglass over the height of the annular strip and, thus, manufacturemineral fibers that have more uniform dimensions and properties. Whenthe first and second annular inductors 2, 5 are in series or inparallel, the heating temperature difference between the top area andthe bottom area of the annular strip is set by acting, for example, onthe position, the number and the diameter of the turns of each annularinductor. When the first and second annular inductors 2, 5 are poweredindependently, the setting of the temperature on the two areas of theannular strip is facilitated because the power can be set independentlyfor each annular inductor.

The top part of the annular strip heated by the first annular inductor 2and the bottom part of the annular strip heated by the second annularinductor 5 can have an area of partial overlap. The area of overlapcannot be total, otherwise the possibility of having a temperaturegradient would disappear.

The mineral fiber forming device also comprises a blowing ring 4,arranged above the centrifuge 1, and suitable for blowing air on thefibers leaving the centrifuge, preferably vertically and downward, so asto turn them down toward a receiving mat situated under the fiberizingdevice. The blowing ring 4 can blow air with an angle of at most 25°relative to the vertical, toward the annular wall 10. The pressure ofthe blowing flow at the output of the blowing ring 4 is preferablybetween 1 and 2 bar.

The mineral fiber forming device may also comprise a second blowing ring3, arranged above the centrifuge 1, in proximity to the web 13. Thesecond blowing ring 3 is suitable for blowing air toward the web 13,preferably vertically and downward. The pressure of the blowing flow atthe output of the blowing ring 3 is preferably between 0.5 and 2 bar.

When the second blowing ring 3 is present, the jets of air blown by thetwo blowing rings 3, 4 meet and create, at their intersection, an areaof turbulences. This area of turbulences is situated in proximity to theannular wall 10. The turbulences produced make it possible to draw evenfurther the mineral fibers than with only the centrifugal force.

As a variant, the blowing ring 4 may comprise a plurality of concentricair outlets but more or less distant from the axis 9. Or else, themineral fiber forming device may comprise a plurality of first blowingrings 4 arranged one above the other, with diameters slightly differentto one another. These variants make it possible to have a plurality ofconcentric air jets which create an area of turbulences favoring anenhanced drawing of the fibers.

These different variants can be combined with one another.

Optionally, the mineral fiber forming device may also comprise aninternal burner (not represented). The internal burner makes it possibleto heat the centrifuge 1 on starting up the mineral fiber forming methodso that the molten glass arrives in a centrifuge 1 which is not cold toavoid the crystallization of the glass. The internal burner ispreferably used only on startup so as to avoid any significantproduction of carbon dioxide. The gas flow rate of the internal burneris less than 5, for example less than 3 Nm³/h.

Preferably, the centrifuge 1 is heated only by the two annular inductors2, 5 without using an internal burner. Thus, the level of carbon dioxideemitted by the mineral fiber forming device can be zero.

Furthermore, the mineral fiber forming device has an efficiency whichcan be as high as 75% or more, instead of only 30% with an internalcombustion burner, and this for comparable operating temperatures. Themineral fiber forming device according to the invention thus allows foran energy saving.

The mineral fiber forming device also comprises, preferably, a mineralfiber gluing ring (not represented), situated under the centrifuge.

According to a variant which is not represented, the mineral fiberforming device comprises a centrifuge that is open on the top, withoutweb or tulip, with only an annular wall sealed at the bottom by abottom. The bottom is fastened to the bottom end of a solid shaft. Thecentrifuge is driven in rotation about its axis of symmetry by therotation of the hollow shaft about the axis of symmetry of the hollowshaft. The molten glass is brought into the spinner via a pipe that isoffset relative to the axis of symmetry of the centrifuge. The pipefeeding the molten glass does not rotate with the hollow shaft and thecentrifuge. The annular inductor 2 is arranged above the annular wall10, so as to heat at least the top part of the annular wall 10. Thedevice comprises a single blowing ring 4, arranged above the centrifuge1, so as to blow air on the fibers leaving the centrifuge, preferablyvertically, so as to turn them down toward a receiving mat situatedunder the fiberizing device. The rest is identical to the embodimentdescribed according to FIG. 1.

The invention also relates to a method for forming mineral fibers byinternal centrifuging. This method implements the device according tothe invention, where the material to be turned into fiber is poured intothe centrifuge 1. The use of the centrifuge according to the inventionthus makes it possible to improve the energy efficiency of the methodand to reduce, even cancel out altogether, the production of carbondioxide.

The mineral fibers obtained by the mineral fiber forming deviceaccording to the invention are used to manufacture thermal and/oracoustic insulation products.

1-11. (canceled)
 12. A mineral fiber forming device comprising: acentrifuge configured to rotate about a rotation axis, the centrifugecomprising an annular wall pierced by a plurality of orifices, the axisof symmetry of the annular wall being the rotation axis; a first annularinductor configured to heat a top part of the annular wall; a secondannular inductor configured to heat a bottom part of the annular wall.13. The device as claimed in claim 12, further comprising a firstblowing ring configured to blow air on the mineral fibers that are aboutto leave through the plurality of orifices in the annular wall to drivethem to a fiber receiving and conveying mat.
 14. The device as claimedin claim 13, further comprising a second blowing ring configured to blowair on an area of the centrifuge situated above the annular wall,cooperation of the first and second blowing rings creating an area ofturbulences in proximity to the annular wall of the centrifuge, the areaof turbulences allowing for an additional drawing of the mineral fibersthat are about to leave through the plurality of orifices in the annularwall.
 15. The device as claimed in claim 13, further comprising at leasttwo first concentric blowing rings of different diameters, cooperationof the first blowing rings creating an area of turbulences in proximityto the annular wall of the centrifuge, the area of turbulences allowingfor an additional drawing of the mineral fibers that are about to leavethrough the plurality of orifices in the annular wall.
 16. The device asclaimed in claim 13, wherein the first annular ring comprises aplurality of concentric air outlets creating an area of turbulences inproximity to the annular wall of the centrifuge, the area of turbulencesallowing for an additional drawing of the mineral fibers that are aboutto leave through the plurality of orifices in the annular wall.
 17. Thedevice as claimed in claim 12, wherein the first and second annularinductors are connected in series or in parallel or are poweredindependently of one another.
 18. The device as claimed in claim 12,further comprising an internal burner configured to use on starting upthe mineral fiber forming device.
 19. The device as claimed in claim 12,wherein the centrifuge comprises a bottom.
 20. The device as claimed inclaim 12, wherein the centrifuge does not comprise a bottom andcomprises a basket.
 21. The device as claimed in claim 12, furthercomprising a mineral fiber gluing ring situated under the centrifuge.22. A method for forming mineral fibers by internal centrifuging,implementing the device as claimed in claim 12, in which the material tobe turned into fiber is poured into the centrifuge.